4,906 research outputs found
Speed and spin differences between the old celluloid versus new plastic table tennis balls and the effect on the kinematic responses of elite versus sub-elite players
This study measured 1) the speed and spin differences between the old celluloid versus new plastic table tennis balls at pre ball-table impact and post ball-table impact when projected with topspin at 7.56 m.s-1, and investigated 2) the effect this has on the kinematic responses of 5 elite versus 5 sub-elite players’ forehand topspin in response to topspin and backspin. Plastic balls were lower in both speed and spin at pre and post ball-table impact compared with celluloid balls but the magnitude of change in speed and spin for each ball material differed. During flight before impact, plastic balls lost 3.98% more speed and 1.24% more spin than celluloid balls. Post ball-table impact, plastic balls showed a greater speed increment (0.69%) and smaller spin decrement (0.19%) than celluloid balls. Differences in players’ kinematic responses to the different ball materials were found only when players returned backspin shots. Players supinated their rackets more by 2.23% at ball-racket contact and produced 3.37% less ball spin when returning plastic compared with celluloid balls; an indication of an early adaptation to the lower spin rate of plastic balls. The lack of differences in kinematic response to topspin may be due to the similar changes in speed and spin of both types of balls at ball-table impact. It is not known if a higher initial ball projection velocity would evoke differences in movement responses from the players post ball-table impact but could be explored in future studies
Influence of Al doping on the critical fields and gap values in magnesium diboride single crystals
The lower () and upper () critical fields of
MgAlB single crystals (for , 0.1 and )
have been deduced from specific heat and local magnetization measurements,
respectively. We show that and are both decreasing with
increasing doping content. The corresponding anisotropy parameter
value also decreases from
in pure MgB samples down to for whereas
remains on the order of 1 in
all samples. The small and large gap values have been obtained by fitting the
temperature dependence of the zero field electronic contribution to the
specific heat to the two gap model for the three Al concentrations. Very
similar values have also been obtained by point contact spectroscopy
measurements. The evolution of those gaps with Al concentration suggests that
both band filling and interband scattering effects are present
Compromised survivorship in zoo elephants
Keeping elephants in zoos is extremely costly, yet does not yield self-sustaining 16 populations. In Europe, which holds c. half the global zoo elephant population, a long17 term decline of c.10% per year is expected in both species, if reliant on zoo-bred animals 18 under historically prevailing conditions. Fitness in zoos is compromised in several ways. 19 Compared with protected in situ populations (Burmese working Asians; Kenyan free20 living Africans), zoo elephants show premature reproductive senescence and -- despite 21 improving adult survivorship for Africans -- die earlier in adulthood than expected. In 22 Asian elephants, infant survivorship in zoos is also greatly reduced relative to Burmese 23 elephants, and furthermore, zoo-born animals die earlier in adulthood than wild-caught 24 conspecifics kept in zoos, via effects ‘programmed’ peri-natally. In this species, being 25 transferred between zoos also increases mortality rates. Both survival and fecundity 26 would need to improve to attain self-sustaining zoo populations. Our findings 27 demonstrate deficits in zoo elephant management, particularly for Asians, and implicate 28 stress and obesity as likely problems
Randomized trial of conventional transseptal needle versus radiofrequency energy needle puncture for left atrial access (the TRAVERSE-LA study).
BackgroundTransseptal puncture is a critical step in achieving left atrial (LA) access for a variety of cardiac procedures. Although the mechanical Brockenbrough needle has historically been used for this procedure, a needle employing radiofrequency (RF) energy has more recently been approved for clinical use. We sought to investigate the comparative effectiveness of an RF versus conventional needle for transseptal LA access.Methods and resultsIn this prospective, single-blinded, controlled trial, 72 patients were randomized in a 1:1 fashion to an RF versus conventional (BRK-1) transseptal needle. In an intention-to-treat analysis, the primary outcome was time required for transseptal LA access. Secondary outcomes included failure of the assigned needle, visible plastic dilator shavings from needle introduction, and any procedural complication. The median transseptal puncture time was 68% shorter using the RF needle compared with the conventional needle (2.3 minutes [interquartile range {IQR}, 1.7 to 3.8 minutes] versus 7.3 minutes [IQR, 2.7 to 14.1 minutes], P = 0.005). Failure to achieve transseptal LA access with the assigned needle was less common using the RF versus conventional needle (0/36 [0%] versus 10/36 [27.8%], P < 0.001). Plastic shavings were grossly visible after needle advancement through the dilator and sheath in 0 (0%) RF needle cases and 12 (33.3%) conventional needle cases (P < 0.001). There were no differences in procedural complications (1/36 [2.8%] versus 1/36 [2.8%]).ConclusionsUse of an RF needle resulted in shorter time to transseptal LA access, less failure in achieving transseptal LA access, and fewer visible plastic shavings
Mesoscopic Fluctuations of Elastic Cotunneling in Coulomb Blockaded Quantum Dots
We report measurements of mesoscopic fluctuations of elastic cotunneling in
Coulomb blockaded quantum dots. Unlike resonant tunneling on Coulomb peaks,
cotunneling in the valleys is sensitive to charging effects. We observe a
larger magnetic field scale for the cotunneling (valley) fluctuations compared
to the peaks, as well as an absence of "weak localization" (reduced conductance
at B = 0) in valleys. Cotunneling fluctuations remain correlated over several
valleys while peak conductance correlations decreases quickly.Comment: 9 pages, postscript (includes 4 figs). To be published in PR
Anisotropies of the lower and upper critical fields in MgB single crystals
The temperature dependence of the London penetration depth () and
coherence length () has been deduced from Hall probe magnetization
measurements in high quality MgB single crystals in the two main
crystallographic directions. We show that, in contrast to conventional
superconductors, MgB is characterized by two different anisotropy
parameters ( and ) which strongly differ at low temperature and merge at .
These results are in very good agreement with recent calculations in weakly
coupled two bands suprerconductors (Phys. Rev. B, 66, 020509(R) (2002).Comment: 4 pages, 4 figure
Thermodynamics of Quantum Hall Ferromagnets
The two-dimensional interacting electron gas at Landau level filling factor
and temperature is a strong ferromagnet; all spins are
completely aligned by arbitrarily weak Zeeman coupling. We report on a
theoretical study of its thermodynamic properties using a many-body
perturbation theory approach and concentrating on the recently measured
temperature dependence of the spin magnetization. We discuss the interplay of
collective and single-particle aspects of the physics and the opportunities for
progress in our understanding of itinerant electron ferromagnetism presented by
quantum Hall ferromagnets.Comment: REVTex, 10 pages, 3 uuencoded, compressed and tarred PostScript
figures appende
Geometrical barriers and lower critical field in MgB2 single crystals
International audienceThe first penetration field sHpd has been deduced from local magnetization and specific heat measurements in magnesium diboride single crystals. For Ha ic, the geometrical barriers (GB) play a dominant role in the irreversibility mechanism. In thin samples, neglecting the GB in this direction would then lead to a large overestimation of Hc1 deduced from Hp through the standard elliptical formula. The lower critical field is found to be isotropic at low temperature (0.11±0.01 T)
Fractal Conductance Fluctuations in Gold--Nanowires
A detailed analysis of magneto-conductance fluctuations of quasiballistic
gold-nanowires of various lengths is presented. We find that the variance
when analyzed for much
smaller than the correlation field varies according to with indicating that the graph of
vs. is fractal. We attribute this behavior to the existence of
long-lived states arising from chaotic trajectories trapped close to regular
classical orbits. We find that decreases with increasing length of the
wires.Comment: 5 pages, Revtex with epsf, 4 Postscript figures, final version
accepted as Phys. Rev. Let
Impact of CKD Progression on Cardiovascular Disease Risk in a Contemporary UK Cohort of Individuals With Diabetes
Introduction: It remains unclear whether an increased progression rate of chronic kidney disease (CKD) adds predictive information regarding cardiovascular disease (CVD) risk. The aim of this study was to evaluate the association between CKD progression, based on estimated glomerular filtration rate (eGFR) slope estimates and the risk for CVD. Methods: We compared the updated eGFR slope calculated over multiple overlapping 2-year periods and the updated mean eGFR. Incident CKD subjects were selected from a prevalent population with diabetes (T2DM). Subjects from the UK Clinical Practice Research Data Link GOLD (CPRD) were followed from CKD diagnosis (n = 30,222) until heart failure (HF), myocardial infarction (MI), ischemic stroke (IS), or a composite end point including all 3 event types (MACE plus), mortality, database dropout, or end of study follow-up. Results: Both the updated eGFR slope and updated mean eGFR were associated with MACE plus and HF. Updated eGFR slope decline of > –3 ml/min/1.73 m2 increased the risk for MACE plus (adjusted hazard ratio [HR] = 1.45; 95% confidence interval [CI], 1.26–1.67), HF (HR = 1.50; 95% CI, 1.27–1.76), and MI (HR = 1.39; 95% CI, 1.01–1.91). Conclusions: This study strongly supports current evidence that CKD is an independent risk factor for CVD. From a clinical perspective, both rate of progression and cumulative status of CKD describe distinct aspects of the cardiorenal risk among persons with diabetes. This evidence is essential to enable more timely and improved use of treatments in this population
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